Heat treatment of manganese hard steel objects



Patented Aug. 7, 1934 NITED STATES HEAT TREATMENT F MANGANESE HARD STEEL OBJECTS Heinrich Resow, Magdeburg,

Germany, assigner' to firm Fried. pp Grusonwerk Aktiengesellscha-rt, Magdeburg-Bumm, Germany ,f Application aecember 2i, rese, serial No. 648,301

lin Germany August 9, 1930 l Claim.

The present invention relates to a process and apparatus for the heat-treatment of'austenitic vmanganese steel objects. Hitherto such objects, containing about 10 to 15 per cent of manganese,

5 have` been heated to about 1000 and quenched as a whole in water and in this way they have been given throughout a hardness of about 200-230 (instead of as previously 280-300) on the Brinell scale. This mode of quenching is, however, un-

suitable for a large number of objects, particulai'ly for those that are subjected on one side to pressure and at the same time to heavy wear. Thus, for example, in the case of crusher jaws, v the crusher teeth must be very hard, i. e. resistant l5 to pressure and wear, whilst their rear side must have great toughness in order that no cracks or breakages may take place due to the heavy stresses in the crusher. Now, as tests have shown, it is possible to treat austenitic manganese steel objects in such a manner that only the portion which is subjected at the same wear remains hard whilst the remaining portion of the article is tough. According to the present invention, this result is attained by slowly cooling the Working portions proper down to carbide precipitation temperature, while keeping the other portions at a high temperature; and then quenching the whole article. In this way there is produced in the working portions proper an austenit ic-carbide, martensite structure which is extraordinarily hard and resistant to wear; while in the remainder of the article a very toughv purely austenitic structure is obtained. It has further `appeared that the Brinell hardness oi the portion first cooled slowly isdisproportionately increased by pressure stressing, from which results a still higher resistance to pressure and wear oi this portion during operation.'

l For the elucdation oi theprocess according to 40 the invention reference is made to 'the accompanying drawing, whereinz- Figure 1 shows a test-piece of steely with 12 per cent oi.' manganese, whilst Figures 2 and 3 depict in cross-section and in plan respectively apparatus for the practicalcarrying out of the process. A

The test piece according to Figure 1 was heated and dipped into water up to the line Av-B, whilst Athe upper part was allowed to cool down in the air. 5 The portion located on the left-hand side .of the line C-D was then cold treated with a pneumatic hammer. In the Brinell test that was then made there were obtained the hardness numbers given.

From these it may be observed that' in the first place the portion cooled in air exhibits a higher Brinelllhardness than that cooled in water and in the' second place the difference between the hardness numbers of the cold-worked portion and o! the unworked portion is considerably time to pressure and' vconduit 3 for compressed air,

, crusher jaw,'is heated to 1000 'that the temperature of about 1000 greater in the case o! the than in the case of that cooled in water.

In this way it is, for example, possible to make a crusher jaw of austenitic manganese steel of which the crusher teeth are extraordinarily hard and resistant to wear in consequence of the slow cooling in air and the austenite-carbide formation resulting therefrom and the rear side whereof receives a purely austenitic structure by reason of the quenching operation and is cons equently tough.

The above-described process may be further improved ii care be taken that the side subjected to wear consists of austenite-carbide and martensite which make the material hard and coldshort, whilst the opposite side is formed of tough austenite. In order toI achieve this, the process may, as 'has been ascertained by tests, be vcarried out as follows with considerably greater speedz- An'article is heated to 1000 C.; the sides of the article that are to remain hard are then cooled 4 down' to a temperature below about 920 C. by means of compressed air, gently acting cooling means. In this way there is formed on these sides an austenitic carbide structure, while the'opposite sides of the article remain heated to about 1000. The entire article is then immediately quenched.

The apparatus for carrying out this process shown in Figures 2 and 3 consists of a. box 1, the upper surface of which is provided with a series of holes 2 and'which is connected to a for example. The box itself rests in a frame 5v which is advantageously provided with rollers '4. The article l to be subjected to the process, for example a C., then with the teeth underneath resting-on the rollers 4 the lower side of the article is cooled below about. 920. During this operation care must be taken C. of the oppositeside, Vwhich ,is to remain tough, is approximately maintained. When the entire article is then'quenched, for example cooled down in a liquid, there is obtained a tough austenitic rear side and hard austenitic teeth the structure of which may also contain martensite.

What I claim is:-

A'process 'for the heat treatment or austenitic manganese steelv articles,'which comprises heating the whole article to about 1000 C.; cooling down portions of the article which are to be subjected to'pressure and wear to carbide precipitation temperature by means of a gentle cooling medium, while the other'portions of the article remain at a high temperature; and then quenching the article as a whole.

' HEINRICH RESOW.

portion cooled in air steam or some other 

